Excavation tools of the types described herein are typically mounted to conventional excavators of the type having a backhoe. The backhoe includes a dipper stick, and the tool is mounted on the outboard end of the dipper stick. The tools are employed for excavation of difficult-to-excavate intermediate substrate, e.g. substrate between the category of loose soil or loose gravel and the category of solid rock. Intermediate substrate requires special tools to be excavated efficiently. Loose soil or gravel can be excavated with a conventional bucket, but a conventional bucket is generally not effective in intermediate substrate. Solid rock excavation generally requires a hydraulic hammer, a rock trencher or blasting, but these methods are not efficient for excavating intermediate substrate. Attempts have been made to develop tools that are effective and efficient in excavating intermediate substrate. Simply stated, there have been several general approaches, e.g., the single tooth approach; the added articulated tooth approach, in which a tooth is positioned behind the bucket; and the multi-tooth bucket approach, where several teeth are mounted on the back side of the bucket, e.g. as described in Arnold U.S. Pat. No. 4,279,085 and Arnold U.S. Pat. No. 4,457,085, or with several teeth mounted along the leading edge of a bucket, the tooth tips in straight line, e.g. as described in Hemphill U.S. Pat. No. 4,037,337, the complete disclosures of all of which are incorporated herein by reference. Each of these approaches has been found to have drawbacks, and none is particularly efficient or effective for excavation of intermediate substrate. In particular, a single tiger or single spike tooth is considered effective for ripping rock because it focuses the force on one concentrated point, thus creating a high pressure to break rock easily. However, the single tiger tooth wears very quickly and must be replaced after a relatively short period of time. The single tiger tooth is also ineffective for ripping the sides of a trench because of the location of the tip. The conventional twin tiger tooth is not as effective for ripping because it tends to share the load over two points; however, it appears to last relatively longer due to the sharing of the pressure between both tips. Also, when the twin tiger tooth is used on the outside corners or edges of a bucket, they allow easier ripping of the trench side wall because on the right side of the bucket, the right tip rips the right side wall, and on the left side of the bucket, the left tip rips the left side wall. In contrast, with a single tiger tooth used on the outside corner of a bucket, the side of the tooth rubs on the side wall and the ripping effect is lessened.